As a monomer for preparing copolymers of fluorinated resins, the demand of HFP has been increased along with TFE. Conventional methods for preparing HFP are pyrolysis of difluorochloromethane(CHClF2, R22) (EP Patent No. 0,287,219 (1988) and U.S. Pat. No. 4,849,554 (1989)), pyrolysis of TFE and octafluorocyclobuthane(C4F8, RC318) (U.S. Pat. No. 3,446,858 (1969)), pyrolysis of polytetrafluoroethylene(PTFE) (U.S. Pat. No. 2,759,983 (1956)), and pyrolysis of R23 (U.S. Pat. No. 3,009,966 (1961)).
The process for preparing HFP by pyrolysis of R22 has low selectivity to HFP due to high selectivity of TFE formation and further, it is difficult to separate pure HFP from an azeotropic mixture of R22 and HFP. Pyrolysis of TFE to produce HFP suffers from a low selectivity to HFP because it mainly produces RC318. Pyrolysis of PTFE has a complicate process, wherein TFE is first prepared by pyrolysis of R22 and then, polymerized to produce PTFE, followed by pyrolysis thereof. And further, even if the selectivity to HFP is higher than that from pyrolysis of R22 or TFE, it is an undesirable method because of expensive unit price.
In the process for producing HFP by pyrolysis of R22 according to the present invention, there has been a limitation in a heat supplying rate to efficiently convert R22 to HFP, is improved by supplying steam pre-heated to 530° C. to 580° C. at a steam generator into a super heating unit to generate steam of high temperature above 900° C. to 1000° C. Then, since this high temperature steam is applied for pyrolysis of pre-heated R22, the heat required for pyrolysis is provided. Further, since a reaction is performed at a temperature of 730° C. to 760° C. which is lower than that of conventional reactions, it prevents the formation of byproducts, which may be produced for an exothermic reaction of TFE, and eventually improves the yield of TFE and HFP.